使用OpenSSL通过OID从X.509证书中提取自定义扩展

我已经能够通过索引从X.509证书中提取自定义扩展名，其中包含：

X509_EXTENSION* ex = X509_get_ext(x509, extension_index);

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如何通过其OID而不是索引提取扩展？

使其能够处理以下内容：

int my_nid = OBJ_create("1.2.3.4", "MyShortObjectName", "My Long Object Name");
int my_idx = X509_get_ext_by_NID(x509, my_nid, -1);
X509_EXTENSION* ex = X509_get_ext(x509, my_idx);

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让它与以下内容一起工作：

int my_nid = OBJ_create("1.2.3.4", "MyShortObjectName", "My Long Object Name");
int my_idx = X509_get_ext_by_NID(x509, my_nid, -1);
X509_EXTENSION* ex = X509_get_ext(x509, my_idx);